Étude de l'évolution hydromécanique d'un carbonate après altération chimique. Application des méthodes de corrélation d'images 2D et 3D à la mesure des champs locaux de déformation lors d'essais mécaniques à différentes échelles.

In order to face the challenge of reducing greenhouse effect gases emission, many solutions have been considered. One of the most studied is the long term geological CO2 storage in deep saline aquifer. These geological structures can be found in sedimentary basins and are defined by there thickness (several hundred meters) and their geographic spread (for instance, the whole Paris basin for the Dogger formation). The second main interest of these geological formations is that the carbonated rocks composing the reservoir are very porous (porosity ranging from 10 to 30%) and present a large enough permeability for an easy injection of fluids. However, the mechanical behavior and long term evolution of these reservoirs after the CO2 injection in the brine are not well established. To this aim, the mechanical and flow properties of these rocks are studied in order to develop predictive evolution models to insure the integrity and the storage capability of the reservoir. The experimental work of this thesis is based on a retarded acid treatment protocol developed and used at IFPEN allowing a homogeneous dissolution of the samples. The goal is to study the evolutions of the hydromechanical properties of the Lavoux limestone with the alteration. The description of the flow properties of the sample has been coupled to a microstructural characterization. The pertinent parameters are the porosity and the permeability at the intact and altered states. The permeability evolution has analyzed by an image substraction technique using microtomograph RX images, which allows the visualization of fine particles in the porous network. These particles have also been revealed by laser diffraction on the flush effluents. The microstructural study of the rock after alteration has allow the characterization of the dissolution mechanisms of our rock. The mechanical behavior has been studied by trixial tests performed at three states of alteration and several confining pressures. These tests demonstrate a transition from brittle to ductile failure mechanism induced by the alteration. In order to better understand this transition, we have also performed uniaxial tests coupled with in-situ image acquisition i) with a classical electromechanical press, CCD captors and optical microscopy for the larger scale and ii) with a miniaturised uniaxial rig in a SEM chamber for the micro scale. The digital image correlation technique has been used during the mechanical loading at several scales, ranging from that of the sample to the microstructural scale. The computation of the deformation fields has shown the different patterns of damage or failure associated with different alteration states. A miniaturized triaxial cell, fitting inside a microtomograph RX, has been specifically developed at IFPEN for this study. This cell allows us to work at various confining pressures (we used 5 and 10 MPa) with volume imaging in in-situ conditions during the mechanical loading inside the tomograph. We have thus identified for three alteration states, three failure modes, namely i) the development of a shear band and brittle rupture for the intact sample, ii) a narrow shear compaction band in a three time altered sample and finally iii) a wideshear compaction band in a six time altered sample. Our set of results on mechanical and flow properties (and more specifically, the variation of permeability and the presence of fines particles in the porous network) would tend to demonstrate that alterations greatly affect the microporosity of the limestone, with strong effects on the shear-compactant behavior of the rock.Devant le défi grandissant de diminuer la libération dans l'atmosphère des gaz à effet de serre plusieurs solutions ont été envisagées. Une des plus étudiée est le stockage géologique du CO2 par injection dans des aquifères salins profonds. Ces structures géologiques sont présentes dans les bassins sédimentaires et se caractérisent par leur épaisseur (plusieurs centaines de mètres) et leur étendue géographique (l'ensemble du bassin parisien, par exemple, pour la couche du Dogger). Le second interêt de ces structures est que les roches carbonatées qui les composent sont généralement très poreuses (10 à 30% de porosité) et présentent une perméabilité suffisamment élevée pour faciliter l'injection de fluides. Cependant, le comportement et l'évolution à long terme de ces réservoirs, après l'injection de CO2 dans la saumure en place, est incertain. Aussi, la résistance mécanique et les propriétés d'écoulement de ces roches sont étudiées pour réaliser des modèles prédictifs d'évolution, afin de garantir l'intégrité et la pérennité des sites de stockage. Le travail de cette thèse repose sur un protocole d'acidification retardée, développé et utilisé à l'IFPEN, permettant une altération homogène d'échantillons de carbonates. Notre objectif a été de déterminer les effets de ce type d'altération sur le comportement hydromécanique de la roche calcaire de Lavoux. La caractérisation des propriétés d'écoulement de la roche a été combinée à une étude microstructurale. Les paramètres étudiés sont la porosité et la perméabilité avant et après altération. Les résultats d'évolution de la perméabilité ont été analysés en s'appuyant sur une méthode de soustraction d'images de microtomographie RX, qui permet de visualiser la mobilité de particules fines au sein du réseau poreux. Ces dernières sont aussi révélées à postériori dans les effluents par diffraction laser. L'étude microstructurale de la roche après altération a permis la mise en évidence des mécanismes de dissolution et d'altération. Le comportement mécanique de notre roche à différents stades d'altération a été étudié à l'aide d'essais triaxiaux classiques réalisés à différents états de confinement. Ces essais ont montré que l'altération induit une transition du domaine de rupture fragile vers le domaine de rupture ductile. Afin de mieux comprendre ce comportement, nous avons mené des essais mécaniques uniaxiaux avec observation et acquisition d'images numériques " in-situ " : i) sur une presse électromécanique classique équipée de caméras CCD et de microscopie optique, ii) à l'aide d'un dispositif de compression miniaturisé adapté à l'enceinte d'un microscope électronique à balayage. La technique de corrélation d'images numériques a pu être appliquée tout au long du chargement mécanique à différentes échelles, depuis celle de l'échantillon, jusqu'à celle de la microstructure. Les mesures de champs de déformation ainsi réalisées ont permis de mettre en évidence les modes d'endommagement et de rupture selon l'état d'altération. Une cellule triaxiale miniaturisée pour être montée dans l'enceinte du microtomographe a spécialement été développée à l'IFPEN pour cette étude. Cette cellule nous a permis de mener des essais à 5 et 10 MPa de confinement avec observation volumique " in-situ " par tomographie. Nous avons pu identifier pour trois états d'altération, trois types de comportements à la rupture, avec l'observation i) d'une bande de cisaillement en régime de rupture fragile, ii) d'une étroite bande de cisaillement en compaction, iii) d'une large bande de compaction en cisaillement. L'ensemble des résultats obtenus sur les propriétés mécaniques et sur les propriétés d'écoulement (notamment la variation de perméabilité et la présence de fines dans le réseau poreux) tend à montrer que l'altération affecte fortement la microporosité du calcaire, avec des conséquences quant au comportement cisaillant compactant de notre roche

Application of 2D and 3D Digital Image Correlation on CO2-like altered carbonate

International audienc

Mechanical evolution of an altered limestone using 2D and 3D digital image correlation (DIC)

International audienceIn the context of long term CO 2 sequestration, we present an original laboratory workflow which allows a multiscale analysis of the effect of a chemical alteration on both petrophysical and mechanical properties of a carbonate. The relation between the mechanical behavior and the microstructural evolutions is investigated using the digital image correlation techniques. For this purpose we imaged intact and altered samples during uniaxial and triaxial mechanical tests using optical microscopy, scanning electron microscopy and 3D X-ray microtomography. The porosity increase induced by homogeneous alteration leads to lower elastic moduli and critical stress at sample failure. Furthermore at a same confining pressure we observed a transition from brittle to ductile failure mechanisms with the increase of alteration level. These observations are evidenced by digital image correlation. Altered samples evidenced early strain localization which was not observed in the intact ones. These early localization events induce more compaction at the macroscopic scale and tend to initiate early fracturing

Docteur en Sciences de l'Ecole Polytechnique Mention: Mécanique Présentée et soutenue par

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Pore fabric geometry inferred from magnetic and acoustic anisotropies in rocks with various mineralogy, permeability and porosity.

14 pagesInternational audiencehe ferrofluid impregnation technique combined with anisotropy of magnetic susceptibility measurements (AMSff) is one of the ways to analyze the 3-D geometry of the pore space in a rock and indirectly to infer the anisotropy of permeability. We applied this method on different types of rocks (sandstones and carbonates) with a range of different porosity values (10-30%) and permeability (1 mD to 1 D). To get additional information on both the pore aspect ratio and the directional anisotropy we used another technique, measuring the anisotropy of P-waves velocity (APV) in dry and water saturated conditions. Comparing between both methods shows that despite the good agreement in directional data, inferring the true shape of the porosity is not straightforward. Modeling the presence of an elastic anisotropy in the solid matrix for sandstones allows one to get more consistent values for the pore aspect ratio obtained from both APV and AMSff. However for the carbonate rocks, due to an intricate distribution of microstructures, the aspect ratios obtained show significant discrepancies between the two methods. The ferrofluid method is very sensitive to the quality of the impregnation and suffers from a major drawback which is the threshold size of investigation, limited by the size of the magnetite nanoparticles (10 nm) and probably this method doesn't see all the porosity. On the other hand with acoustic methods, the range of porosity investigated is probably larger but several microstructural attributes can contribute to the elastic anisotropy which makes the pore shape effect more difficult to decipher. Therefore, we promote the combined use of both methods in order to get more reliable information on the pore shape in porous media

Utility of biomarkers in prediction of response to ablative therapy in Barrett's esophagus

BACKGROUND & AIMS: Photodynamic therapy (PDT) has been shown to be effective in the treatment of high-grade dysplasia (HGD)/mucosal carcinoma in Barrett's esophagus (BE). Substantial proportions of patients do not respond to PDT or progress to carcinoma despite PDT. The role of biomarkers in predicting response to PDT is unknown. We aimed to determine if biomarkers known to be associated with neoplasia in BE can predict loss of dysplasia in patients treated with ablative therapy for HGD/intramucosal cancer. METHODS: Patients with BE and HGD/intramucosal cancer were studied prospectively from 2002 to 2006. Biomarkers were assessed using fluorescence in situ hybridization performed on cytology specimens, for region-specific and centromeric probes. Patients were treated with PDT using cylindric diffusing fibers (wavelength, 630 nm; energy, 200 J/cm fiber). Univariate and multiple variable logistic regression was performed to determine predictors of response to PDT. RESULTS: A total of 126 consecutive patients (71 who underwent PDT and 55 patients who did not undergo PDT and were under surveillance, to adjust for the natural history of HGD), were included in this study. Fifty (40%) patients were responders (no dysplasia or carcinoma) at 3 months after PDT. On multiple variable analysis, P16 allelic loss (odds ratio [OR], 0.32; 95% confidence interval [CI], 0.10-0.96) predicted decreased response to PDT. BE segment length (OR, 0.71; 95% CI, 0.59-0.85), and performance of PDT (OR, 7.17; 95% CI, 2.50-20.53) were other independent predictors of loss of dysplasia. CONCLUSIONS: p16 loss detected by fluorescence in situ hybridization can help predict loss of dysplasia in patients with BE and HGD/mucosal cancer. Biomarkers may help in the selection of appropriate therapy for patients and improve treatment outcome